Latent catalyst effects were investigated to improve the physical properties of halogen-free epoxy molding compounds (EMCs) for semiconductor encapsulation. In this study, biphenyl-type resins were used as the epoxy and hardener resin for halogen-free EMCs to obtain hi-h flame-retardant properties and high filler contents. Latent catalyst effects were examined with two kinds of EMC compositions, halogen-free EMCs and conventional EMC compositions. We used triphenylphosphine-benzoquinone salt (TPP-BQ) as a latent catalyst. Spiral flow and gel time were measured to investigate the change in moldability with the latent catalyst. We measured package fail, Moisture absorption, and delamination for reliability evaluation and flexural strength, flexural modulus, and adhesion for mechanical properties to examine latent catalyst effects. An improvement in moldability, reliability, and the mechanical properties were observed in two types of halogen-free EMCs with TPP-BQ as a latent catalyst. These phenomena were seen in conventional EMCs, including o-cresol novolac epoxy resin. The cure kinetics of these systems were investigated by differential scanning calorimetry with an isothermal approach to explain these phenomena. The results indicate that the improvement in moldability in halogen-free EMCs with TPP-BQ was due to the low conversion rate of this system, and the increase in mechanical properties was attributed to the high conversion of curing reaction. (c) 2005 Wiley Periodicals, Inc.